Technical Field
The present disclosure generally relates to a machine for machining a moving object. More in particular, the present disclosure relates to a machine for continuous-cycle cutting of metal bars, such as, for example, steel tubes.
Description of the Related Art
Machines for continuous-cycle cutting of tubes are known, i.e. machines which cut tubes of the desired length while the tubes themselves are moving. A continuous-cycle cutting machine comprises means for conveying the tube to be cut along an advancement direction and comprises a slide that moves along a forward and return direction parallel to the advancement direction. The slide supports a cutting device. The conveyor means are for example a conveyor belt, while the cutting device is for example a milling cutter.
The slide travels in a forward stroke until arriving in the proximity to the tube in the position calculated for cutting it, then it is synchronized with the conveyor means moving at the same speed as the speed of the tube moving on the conveyor means: in this condition the cutting device performs the cut of the tube in a direction that is perpendicular (or, more in general, inclined) with respect to the advancement direction.
European patent number 1462200 describes a machine for continuous-cycle cutting of welded tubes. The cutting machine comprises a microprocessor controlling (by means of driving means) the cutting slide such that the latter has an acceleration A′ with a law of motion in the cutting cycle which is a derivable function, as shown schematically in FIG. 1 with a dashed line. Moreover, a sinusoidal (or 7th degree polynomial) speed trend V′ of the slide is used for the connecting portions between the acceleration value A′=ac′ (greater than zero) and A′ equal to zero and between the acceleration value A′ equal to zero and A′=−ac′ (smaller than zero), as schematically shown in FIG. 1 with a solid line. Moreover, it is possible to observe that the maximum absolute value of the acceleration/deceleration in the forward phase (see the time instants comprised between t0′ and t1′ and between t4′ and t5′) is equal to the maximum absolute value of the acceleration/deceleration in the return phase (time instants comprised between t5′ and t6′ and between t10′ and t11′): this maximum absolute value has been indicated in FIG. 1 as a′c.
The Applicant has observed that in patent EP 1462200 the maximum absolute value of the acceleration/deceleration of the cutting slide in the return phase (see for example the value −a′c of point P3 and the value a′c of point P4 of the dashed curve in FIG. 1) is such as to cause accelerations and decelerations of the cutting slide which are not optimized; consequently, the moving parts of the cutting machine undergo mechanical stresses which cause wear of the moving parts, thus reducing the reliability of the cutting machine.